X-ray generator



H. K. HUPPERT ET AL X-RAY GENERATOR Sept} 8, 1936. 2,053,792

Filed July 19, 1933 2 Sheets-Sheet 1 In III/0170 INVENTORS,

HENRY K. HUPPERT.

THOMAS H. FORDE.

ATTORNEY 4o RECTIFIER. L

16 s 4 so @vg $52 f;j"s c .32 M 49 Q50. III NI I p 1936- H. K. HUPPERTET AL 2,053,792

X-RAY GENERATOR Filed July 19 1933 2 Sheets-Sheet 2 .llym

RECTIFIER. g RECTIFIER.

I INVENTORS, HENRY K. HUPPER T.

THOMAS H. F ORDE.

50 ATTORNEY Patented Sept. 8, 1936 earns-r OFFICE X-RAY GENERATOR HenryK. H'uppert and Thomas H. Forde,

. San Francisco, Calif.

Application July 19, 1933, Serial No. 681,104

3 Claims.

Our invention relates to X-ray generators having a-hot cathode; and moreparticularly to such tubes having a control element" therein whereby thedirection and amount of the cathode ray stream between anode and cathodemay be changed at will independently of the cathode or anode'supply.ljhe invention further relates to methods of generating X -rays havingpeculiar characteristics, this application being a continu- 0 ation inpart of our prior application, Serial No.

580,836, filed December 14, 1931.

Among the objects of our invention are: To provide an X-ray' tubewherein the electron Stream can be controlled independently of theano'de'and cathode supply; to provide an' X-ray tube in which a spacecharge is present during a substantial part of the time that X-rays arebeing generated; to provide an X-ray tube which may be madeself-oscillating at high frequencies;

' to provide" an X-ray tube in which the size of the focal spot may bechanged electrically; to provide an X-ray tube in which the position ofthe focal spot may be changed electrically; to

provide an X-ray tube in which the envelope is '25 effectively protectedfrom secondary electron bombardment; to provide an X-ray tube in whichstray X-rad'iation outside the main beam is reduced. to a minimum; toprovide an X-ray tube or increased efficiency; to provide an X-ray tubeof simple construction and in which the elements are in concentricrelation; to provide an X-ray tube having a minimum band of X-raywavelengths" in the active beam; and to provide a greatly improved X-raygenerator and novel 35 methods of operation.

Other objects of our invention will be apparent or will be specificallypointed out in the description forming a, part of this specification,but we do not limit ourselves to the embodiment 0 of our inventionherein described, as various forms may be adopted within the scope ofthe claims.

Referring to the drawings, which illustrate sev eral' embodiments of ourinvention:

Figure 1 is a view in elevation of the elements of a right angle X-raytube embodying our invention, the envelope being cut away and shown insection.

50 Figure 2 is an enlarged plan view of the cathode and controlelectrode, the cover of the control electrode being removed.

Figure 3 is an enlarged view partly in section and partly in elevationshowing the relations of anode, cathode and. control electrode,

Figure 4' is a sectional view of another embodiment of our invention.

Figure 5 is a schematic diagram of? a circuit in which the tube may beused.

Figure 6 is a schematic diagram of another 5 embodiment of our inventionas used to control the position of the focal spot.

Figure 7 is a schematicdiagram of the tube of our invention as used inan oscillating circuit.

Our invention, broadly considered from the 19 point of view ofapparatus, comprises an X-ray tube containing an annular cathode, and-ananode, preferably of conical shape positioned in the axis of the circledescribed by the cathode, the apex of the anode cone being usuallyplaced in substantially the center of the circle. The cathode isenclosed by a control electrode having preferably a concentric annularaperture between the cathode and anode. The control electrode is adaptedto be separately energized to give con- 20 trol of the electron howtothe anode. It may also be desirable to make use of the control thusafforded to cause the X-ray tube to be selfoscillatory at highfrequencies by the use of proper exterior circuits, thus giving rise toan X ray beam pulsating at high frequencies.

Considered broadly as to methods involved, we are able to-control thecathode ray current and consequently the intensity of the X-ray beam bychanging the thickness of the cathode ray stream. We also utilize themethod of changing the thickness of a discoidal cathode ray stream tochange the size of the focal or impact spot, and we also change thedirection of the discoidal stream to change the position of the 3 focalspot. We may desire to make the X-ray beam pulsate at high frequenciesby making the cathoderay current self-oscillatory, thereby producing anX-ray having peculiar results of unexpected character.

In the ,detailed description of the preferred forms of our inventionwhich follows, wherein certain relative dimensions are shown anddescribed, and certain specific circuits are menti'oned, it is to beunderstood that these dimensions are relative only and may be departedfrom widely in order to adapt the apparatus to various kinds ofradiographic, therapeutic, diagnostic or experimental uses, and thatother equivalent circuits may be substituted for the specific onesdisclosed, without departing from the spirit of this invention.

It is also to be understood that we do not at this time, desire to ofierany extended explanation or discussion of the theories involved in thiscontinued experimentation, and coordination and assembly of widespreadobservations. In such a rapidly advancing. field, additional data mightV well modify or completely change presently'held theories-without,however, necessitating change or modification of apparatus or methodbeyond the scope of the appendedclaims;

In the drawings, referring especially to Figures "1, 2, and 3, anenvelopell is;provided with an" fanode arm l2 and a shorter cathodearmfl3. j

It ispreferred that the armsbe placed at right I y [from an' alternator50 either directly whereby angles, leaving a radiation "window 'Mffree1of 7 1 obstructions. V 1

'.brolts 20;. r '3 Thefcontrol electrode assembly comprises aAlcathodesteni l5j'is sealed in the endorsthe cathode arm and supports acontrolrelec trode'assembly I6 by means .of control'rods l'l fastenedtota band l9'clamped to the. stem' by hollow cup-shaped body which has;acover 2|, acircumferential side wall- 22 anda" face plate 24,,thelatterebeing' provided with a cone shaped radiation aperture ,25positioned to face the ra-- jdiation ::win'dow: l4. Thetcover 2I,which-may I be removed bytaking out screws 26,- ,and theinneri'surfaceof'the faceplate are preferably dished sufliciently toform an. annular aperture '21isomewhat narrower in width than the inte-;rior:'chamberiwidth next the side wall.)

cover fl:isprovided with' a .central anode aper-' r r. """Cathodesupports'29are sealed to and; thereby positioned parallelto the controlrods. H'- by a spacer. ;3n{pref erably formed'fro n quartz; These fleadsiproject' into the control electrode chamber through cathodesupport apertures 3|; 1 v 'Anannular cathode 32 preferably formed from'aj tantalum or. tungsten coilis fastened to the leads concentriciwith.the side wall 22v aboutrnidwaybetween thesidewalland the annular apere V*i turegizl:"Quartz-unlike insulators 34, set'around the side wall carry'hooks 35 bywhich-thecathode is maintained in'its concentric positionsCathode leads 36 and a control. lead 31 are fsealed-throughia pinch 39of the'cathode stem and connect with the cathode supports and aco-ntriol rodprespectivelyq g In theian'ode'rarm; a long anode'rod 40,pref-1 erably of heavy copper is provided with a welded skirtr ll ofa'material which will seal-to the 5 envelope matelial'toform a 'ring ,seal 42, with a" reentrant tube 44. 1

Thetanode rod continuesjo n in? the central axis of the tube -andterminates in an. anode plugfl45 preferably oftungsten set into and fas-'The tip of-the t tened to the-endof the rod, and exposing alcon edtargetsurface 46, .1 V

l W rg et co ne projectsthrough the anode aperture, 28 in 1 the controlelectrode coverbyan amountwhich maybe varied, V as will I be later;described, but in any event, :it is; 'pren erable thatthe tip of; the(cone. be in the axis of the circle described by the annular .-catho-de.

Itis also desirableft'o makeI-the .totalfdiameter o f the anode rodsomewhat larger than the cover aperture so that the shoulders of theanode rod 'will shield the anode endi'of the, tube-from stray]X-radiation, primary or secondary electrons from inside. thecontroLelectrode assembly. .A slightly different embodiment ofourinvention i's'shown in Figure 4; Here the anode arm leakage in thesupports,

, the negative potential will l2 and the cathode arm 13 are in line, theradiation opening in the control electrode being directed toward a sidewall of the envelope, and the anode rod being provided with a rightangle bend 41 to place the coned target surface in the ings showing theanode tip in different degrees of insertion.

InFigure 5, the cathode 32 is energized by asource. 49, the anode beingusually energized the tube becomes self-rectifying, or preferablythrough a'rectifier, as is well known in the art.

The control electrode is maintained at a potential difierent from thatof the cathode by a biasing source 55;: or insome cases by a resistor 52I which will; then cause the control electrode to become nfigative due.to accumulation of electrons during operation.

7 In some cases it may be desirableto let the control electrode floatfree without connection, in which case it will charge up to a highnegative potential, but will notusually block theanode current at theanode potentials in vogue, as there is always someslight In operationthe annular cathode an annular cloud of electrons, some of whicharedrawn through the annular aperture to the coned target surface andothers are returned to the cathode, a discoidal stream of =electronsbeing. formed Which is dense near the cathode and thinning out towardthe anode. This cloud of electrons constitutes thespacecharge, and itsformation is encouragedfby the enclosure of the cathode. Varyingpotentials placed on the control electrode will control the amount ofcurrent reaching" the anode; in general, a negative potential decreasingthe. current, and a less negative potential increasing it. l I

Due to the shape of the annular aperture however, placing a potential onthe control electrode will also change the dimensions or shape of thestream. The ,equipotentiallines produced when he. control electrode isenergized are indicated by the numeral 54 and the generalpath of thestream sectio-nby the dotted line 55. Increasing the negative potentialonlthe control electrode will make the stream thinner, and decreasingthicken itQ Th'u s the thickness of the stream can be controlled, theend result being the same .as if the physical annular aperture 21 wereto be changed in dimension. We have therefore given the name ofelectricalaperture to the condition existing in the annular aperturewhen energized.

Several results apart from: the gross control of current may beaccomplished by the use of the electrical aperture. By changing thethickness of the stream a greater or, less amount of target surface maybe bombarded,'thus changing the size of .the focal spot, for-varioustypes .of radiography. The shape ,of the spot willbe determined by theposition of the coned target surface. If placed so that the apex of thecone passes completely through' thestream, the spot will be a ringwhich" maybe made narrow or 'wide, If the cone is retracted as in Figure5,

of varying size allot which adds to the versatility f thedevice.

In case the tip is withdrawn along the axis of the circle away from thecenter as in Figure 5,

pass out of the electrical aperture, thereafter the anode turning towardthe tip. As the electrons are rapidly increasing their velocity, theydrive close to the center of the circle before turning to bombard tip.In other positions where the tip is close to the center, practically nodishing occurs. .1

In Figure 6 a circuit is shown, as in Figure except thatthe upper andlower portions of the control-electrode are electrically distinct and aseparate biasing source 56 is shown for the upper portion. By adjustmentof potentials, both the direction and amount of the stream may becontrolled to produce conditions only obtainable in the previouslydescribed tube by physically withdrawing or inserting the anode tip intothe stream, a construction which is not easily feasible in a singletube.

Figure 7 represents a circuit in which the tube as above described willoscillate. The circuit is l the well known tuned grid tuned platecircuit, a

control resonant circuit 51 being placed in series with the controlbias, and an anode resonant circuit 59 in series between the anode andcathode. A blocking condenser 60 is preferably placed between the anodeand the resonant circuit and the high voltage parallel fed from theusual transformer 6| through the rectifier.

We have found that the tube as described can be set intoself-oscillation at a frequency of 7,500 kilocycles without difficultyand when it is oscillating the high frequency pulsating X-ray beamappears to have a penetration quality somewhat difierent than that to beexpected from the actual applied voltage. Such penetration has beenexperimentally observed and therapeutically used, but we are not at thistime ready to express an opinion as to the reason therefor.

However, as the frequency of oscillation is determined by the tuning ofthe control electrode circuit, the reaction of the anode circuit beinginductive, variation of the tuning of the anode resonant circuit willchange the relative phase of the anode potential and anode current,without substantially changing the oscillation frequency. This change inphase relation gives rise to internal conditions diifering widly fromthose in the ordinary X-ray tube, and may well modify ant phaserelations produce a pulsating X-ray beam having entirely difierentcharacteristics than that produced by an ordinary tube having the anodeenergized by high frequency alternating current.

The X-radiation of the device however, does have a homogeneity, to whichwe believe there is a reasonable explanation. It is well known that theX-rays from a tube consist of two main classes; the heterogeneousspectrum of general radiation within a range of quality which dependssolely on the speeds of the parent electron streams;-and the homogeneousor monochromatic radiations which are characteristic of the targetmetal.At high voltages the bulk of the radiation is of the latter type, but intubes using unfiltered alternating clurrent, there is a large componentof the softer heterogeneous rays generated as the anode voltage rises tothe point where the homogeneous radiations begin, the relative amountsdepending on the wave form applied to the anode.

By creating a space charge, and by using a strong negative potential onthe control electrode, we are able to prevent anode current from flowingduring the low voltageportions of the wave at the beginning and end'ofeach half cycle, and thus greatly reduce the amount of the socalledgeneral radiation, leaving the bulk of the X-ray beam hard rays of thehomogeneous type. The efiectiveness of the tube and the therapeuticefiiciency is thus greatly improved.

It should be observed that high negative potentials may be used on thecontrol electrode without changing the quality or hardness of the X-radiation from the anode. The net potential difference between the anodeand cathode is the dominating factor, controlling as it does, the speedof the electrons bombarding the anode. The velocity of the electronstream will be held down by the potential of the control electrode whilethe electrons are within the limits of its influence, but after theyescape through the electrical aperture and pass toward the anode, theyare accelerated again at a rate which will land them against the anodewith not less than the same velocity as they would have if they hadstarted from the cathode and proceeded to the anode without influence ofany control electrode or control potential.

There is also experimental evidence to indicate that the quality orhardness of the final X- ray is such that greater penetration for agiven anode-catrode potential difference is obtained from our tube withthe cathode emission controlled by the electrical aperture of ourinvention. While we realize that the quality or hardness is customarilysaid in textbooks to be entirely determined by the anode potential, wehave obtained reliable experimental evidence of greater effectivepenetration in the rays emitted from the tube as described, although wedo not at this time care to ofier an explanation of that discovery.

Several further features of our invention should be pointed out. Thecathode and focal spot being enclosed, and the walls of the controlelectrode being of sufficient thickness to stop casual X-rays,practically no X-radiation passes out except through the radiationaperture. The cover 2| of the control electrode, although it may besomewhat thinner than the rest of the control electrode, preventsX-radiation along the back of the tube, and as the diameter of the anoderod is larger than the aperture in the cover, complete shielding isprovided. Furthermore, the enclosed construction prevents strayelectrons from striking the glass to form hot spots and eventualpuncture. The construction as shown therefore, completely shields theenvelope from both the cathode rays, and the X-rays except through theproper path, and no auxiliary internal or external shields are necessaryfor the protection of the operators from stray radiation.

It is also possible to regulate the anode current to provide a uniformoutput even though slight chargeor control; such? variatio-n'svin linevoltage change the cathode temperature with resultant V fluctuations ofmilliampera'ge and much: elaborate compensating equipment;

We claim:

;. 1'.- Themethod: of" generating: X-rays which comprises the steps of;forming. anannular'clo'ud of-electrons, 1 directing said electronsinwardly to a common center, intersectingsaid cloud adjapcent'saidcenter to produce; a streamof X-r'ays directed outwardlyalongiaaline perpendicular to t the plane-of the-"electron:path;andtvaryingthethickness of' the electron stream to-= vary' the d1- 'ameter of theX-ray stream.

-2.- Themethodof controlling-:the X-rayb'eam emitted'oircumferentiallyfrom-a conical anode,

irregularities inlline *v'oltage' maywocc'ur. In ordinary tubesopera-ting at saturation-without space which comprisesformingran'annulai cloudofelectrons concentric with the axis'o'f said:anode, di resting"said:elctronsinwardly to bombard the coneof-"saidanode; and varying the thickness of the;e1ecl7r0n stream todefine-vtheamount-of anode surface bombardedrby said electrons.

4, Tlie'method of generating X-rays'whjch comprises the steps: offorming an annular cloud of electrons;-, directingsaid electronsinwardlyito a common center; intersecting said cloud: adjacentsaidacentertdproduce a stream of; X-rays directed outwardly along a;line perpendicularto the plane of" the electron pathl-zand varying thethickness of the electron stream to control the X-rays, pro-,- duced;

K. HUPPERT. THQMAS H.- FORDE'.

